1. Technical Field of the Invention
This invention relates to electrolytes and more particularly to alkaline electrolytes as employed in fuel cells, industrial electrolytic cells such as cells for chlorine electrolysis, and metal-air batteries.
2. Background Art
U.S. Pat. No. 3,948,681 of Barger et al "Fuel Cell Utilizing Direct Hydrocarbon Oxidation" describes a fuel cell with an electrolyte comprising CF.sub.3 SO.sub.3 H.H.sub.2 O, which is the monohydrate of trifluoromethyl sulfonic acid. Other electrolytes described there include higher homologues of the monohydrate and different acid to H.sub.2 O ratios. No suggestion of mixing trifluoromethane sulfonic acid (TFMSA) with other electrolytes appears in that patent. The cathode and anode are constructed from a noble metal such as platinum mixed with carbon and polyethyleneterephthalate (Teflon) and supported on graphite. U.S. Pat. No. 3,379,573 of Gershberg for "Fluorinated Polymer with Fluorinated Surfactant and Fuel Cell Therewith" describes a fuel cell with an electrolyte of KOH plus ammonium perfluorocaprylate and porous electrodes with electrodes of Pt, Pd or Ag. Alternatively, ammonium perfluoronyl sulfonate is the surfactant in the electrolyte.
In U.S. Pat. No. 4,118,550 of Koch for "Aprotic Solvent Electrolytes and Batteries Using Same" Col. 7 mentions the use of a lithium salt of TFMSA as a solute in an electrochemical cell having a lithium negative electrode, with an electrolyte comprising an ionically dissociable solute in the form of a lithium salt and a solvent for the salt. There is no suggestion of adding TFMSA to an electrolyte.
A problem with batteries, fuel cells and industrial electrolytic cells is that limited solubility of oxygen tends to limit current for a given potential. This results in excessive polarization of the cathode (the oxygen electrode). The total cell voltage in fuel cells, metal-air batteries, and industrial electrolytic cells can be resolved into components which add as EQU E=E.degree.+.eta..sub.a +.eta..sub.c +IR
where I is the total current flow, E.degree. is the thermodynamically reversible potential, R the resistance due to the separator and electrolyte and .eta..sub.a and .eta..sub.c the overpotentials of the anode and cathode respectively.
In accordance with this invention, TFMSA is used as an additive to alkaline electrolytes to lower the cathode polarization .eta..sub.c in the types of cells including fuel cells, batteries and industrial electrolytic cells. Preferably, at least one of the electrodes is a gas-fed porous structure incorporating a catalyst of a material selected from the group consisting of gold, platinum, palladium and silver or a nonmetal such as Ni and Co spinels.